The eclosion hormones of silkmoths is a peptide hormone that has a number of neurally related effects: 1) It releases the behavior associated with the escape from the pupal cuticle; 2) it "turns-on" adult behavior; and 3) it triggers muscle degeneration in the abdomen. The hormone acts directly on the CNS and its action is mediated through an increase in cyclic GMP. Target neurons in the moth nervous system will be identified by the binding of radiolabeled hormone. Also, using immunocytochemistry, cells that show increases in cyclic GMP will be identified. Various aspects of the early action of the eclosion hormone on CNS will be examined in vitro. These include the involvement of calcium ions in the response, the role of cyclic GMP dependent phosphorylation of nervous system proteins, and the role of macromolecular synthesis in the late actions of the hormone. The neural circuitry involved in behaviors that are influenced by the hormone will be studied. Attempts will be made to relate the hormone induced changes in the target cells to this circuitry.